Things to know about clean rooms

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Things to know about clean rooms

If anyone ever saw an Intel ad, how would they ever see an advertisement for Intel engineers wearing tight-fitting suits from head to toe dancing in the room, looking like astronauts dancing on a spaceship. And if there is a bit of technical interest, then you are curious to wonder what they wear to do, and if you love it a little more, how would you ever dream of wearing that outfit to Work like them, an interesting job? Please, that is the protective clothing when working in a clean room (such as clean room of Intel semiconductor technology for example), and when working to wear it, it is not easy. You will ask, what is the clean room? Why must there be a clean room? Hopefully this article will help you have an initial understanding of clean rooms.

1. What is a clean room?

If you need to say it simply, you can answer that "clean room" is a very clean room. Clean rooms (English is cleanroom - a compound noun), as defined by ISO 14644-1 standard are: "As a room where the concentration of suspended particles in the air is controlled and it is built and used. used in a structure so that the presence, production and maintenance of particles in the room are reduced to a minimum and other elements in the room such as temperature, humidity, and pressure can be controlled and controlled. ". Originally in English: "A room chứa concentration of airborne is controlled, and constructed and used in mà a Manner to minimise the introduction, generation and retention of particles inside the room and the relevant parameters chứa other, vd temperature, humidity, and pressure, are controlled as neccessary. ”[1] In simple words, the clean room is a closed room in which the amount of dust in the air is limited to the lowest level to avoid causing contamination. research, manufacturing and manufacturing processes. At the same time, air temperature, pressure and humidity are also controlled and controlled to be the most beneficial for the above processes. In addition, the room is guaranteed to be sterile, without harmful gases in accordance with its "clean" meaning.

2. The history of clean rooms, the need for clean rooms

The clean room used for the first time is in the medical field. In the beginning, the research works of Pasteur, Koch, Lister and other pioneers have shown that infection is the cause of many diseases, but one of the causes of infection is loss. hygienic in the environment. For the first time in the 1860s, Joseph Lister (a professor at Glasgow University) set up a closed room system to limit dirt, fight infection at the Royal Glasgow Hospital Institute (Royal Infirmary, is an institute founded by Glasgow University, today called Glasgow Western Infirmary). This is the first primary clean room [1]. And the clean room system used for production began to be used during the Second World War to improve military guns and weapons. Until now, the clean room was only at a primitive level to be cleaned by a simple vacuum and hygroscopic system, far from today.

Next, the clean room was developed one step further by promoting from the nuclear, biochemical and biochemical research industries that led to the introduction of air filtration systems. Clean rooms with large capacity, good air filtration system started to develop strongly in 1955. Electronic company Western Electric Company (Winston-Salem, USA) encountered problems with wrong products. due to the presence of dust particles in the air. The requirement for them is that clean rooms are not contaminated with dust, and since then the clean room system has been developed, with filtration systems, control systems, protective clothing to prevent dust and dirt in the room ... developed as it is today. And now, clean room is used for many fields: medical, scientific and technical materials, electronic components, physics, chemistry, biology, precision engineering, pharmacy ...

3. Clean room standards

The first standard of a clean room is the amount of dust, which is how high the content of suspended particles in the air is controlled (of course, the dust must be cleaned). If we compare figuratively, the diameter of a human hair is about 100 m, the dust in the room may have a diameter of 0.5 to 50 .

Cleanroom standards were first introduced in 1963 in the United States, and have now become common standards for the world. These are the standards that regulate the amount of dust particles in an air volume unit. It is divided into dust sizes and room types defined by the number of dust particles larger than 0.5 m on a volume of 1 cubic foot (ft3) of room air.

a) Federal Standard 209 (1963) [1]

 This standard was first defined in 1963 (named 209), and then continuously improved, completed into 209 A (1966), 290 B (1973) ..., until 209 E (1992).

b) Federal Standard 209 E (1992) [2-3]

This standard defines the content of suspended dust in air according to the standard unit (air volume unit is m3). The clean room classification is defined by the logarithmic scale of dust content with a diameter greater than 0.5 m. Below is the standard table FS 209 E.

Class

maximum particles/ft³

ISO equivalent

≥0.1 µm

≥0.2 µm

≥0.3 µm

≥0.5 µm

≥5 µm

1

35

7

3

1

 

ISO 3

10

350

75

30

10

 

ISO 4

100

 

750

300

100

 

ISO 5

1,000

     

1,000

7

ISO 6

10,000

     

10,000

70

ISO 7

100,000

     

100,000

700

ISO 8

Table 2. Dust limit in 209 E standard (1992).

This standard table has been officially canceled by the US Department of Commerce since September 29, 2001 but is still widely used.

c) ISO 14644-1 standard [3,4]

 International Standards Organization (ISO) has defined international standard cleanroom standards. ISO 14644-1 standard was released in 1999 named "Classification of Air Cleanliness" (Classification of Air Cleanliness). Clean room types are defined based on the expression: with: Cn¬ is the maximum permissible content (in number of particles / m3) of badger dust air greater than or equal to the size of consideration. N is the ISO classification number, does not exceed 9 and the minimum allowable index is 0.1 D is the diameter of the particle in 0.1 here is the constant with the dimension made. Thus, it is easy to determine the dust content limits from the above formula and easily classify each level of clean room.

Class

maximum particles/m³

FED STD 209E

 

equivalent

≥0.1 µm

≥0.2 µm

≥0.3 µm

≥0.5 µm

≥1 µm

≥5 µm

ISO 1

10

2

         

ISO 2

100

24

10

4

     

ISO 3

1,000

237

102

35

8

 

Class 1

ISO 4

10,000

2,370

1,020

352

83

 

Class 10

ISO 5

100,000

23,700

10,200

3,520

832

29

Class 100

ISO 6

1,000,000

237,000

102,000

35,200

8,320

293

Class 1000

ISO 7

     

352,000

83,200

2,930

Class 10,000

ISO 8

     

3,520,000

832,000

29,300

Class 100,000

ISO 9

     

35,200,000

8,320,000

293,000

Room air

Table 3. Dust content limits in ISO 14644-1 [1.4].

It should be noted that the level of air pollution in the room depends on the dust particles generated in the room activities, not just the fixed number of rooms. Therefore, in the standards of the room, continuous cleaning systems are required and there are also regulations on room size and number of people, the number of possible activities in a clean room. In addition to these standards, each industry can also have its own requirements, such as working on the semiconductor circuit industry that is different from the medical industry ... We remember that the semiconductor industry manipulates parts. The material element is up to micron size, so it is very demanding about small dust content, while the health sector requires a high level of cleanliness and air conditioning to prevent infection ...

4. Clean room designs

4.1. Turbulently Ventilated Cleanroom (Turbulently Ventilated Cleanroom)


The ventilation principle of this clean room is similar to most common air-conditioned rooms such as offices or shops. The air (clean) provided by the air conditioner is radiated through the ceiling diffusion system (pictured).

It is called "chaotic venting" because it is not possible to move randomly and chaos in a room through a diffusion system or a "spray" system.

The air spray system is often encountered in traditional chaotic clean room systems. This type of system usually provides straight air flow and is capable of controlling contamination well under the filter. This spraying system may provide better conditions under the supply zone, but therefore inferior to the surrounding areas of the room.

4.2. Full directional clean room (Unidirectional Cleanroom)

The clean room system with the vented ventilated type usually only achieves the standard cleanliness up to ISO 6 level in the production process. In order to achieve better conditions during operation, it is necessary to dilute the production of particles. This can be achieved by using a completely straight air stream.

The figure above is a section of a clean room design with vertical air flow and is operated in a closed manner like pistons. Therefore, this air stream helps to remove the contamination. When circulated to the door, this air stream will be transported in the stream and again circulated through filter systems. This system is much more advanced than a chaotic exhaust system because of its ability to eliminate rapid contamination. Gas flow velocity is usually from 0.3 m / s to 0.6 m / s. However, this type of clean room has a much higher cost and operating cost than a chaotic ventilation room.

Another type of directional clean-room system is a horizontal airflow system with the same way that air flows from one side of the wall to the high-efficiency filtration system and blows through the room, then goes back after hit the opposite wall. Because the wall area is usually much smaller than the ceiling area, the cost of this type of room is also lower than that of vertical air flow.

Horizontal air circulation system is not as common as a vertical system although it is cheaper for reasons related to contamination (we see two ways to dilute contamination in two types of horizontal and vertical rooms. In a room with vertical flow, the dust will be pushed vertically to the floor, and blow down the air and non-contamination locations from one location to another as well as from this person. And the horizontal air circulation system can lead to dirt being blown from one location to another, or from the front person (air flow direction) flying to the rear person.

The vertical air flow clean room system is commonly used for semiconductor industry and material technology in recent years. In semiconductor components and materials technology, air is filtered with very high cleanliness and blown in the direction from the ceiling down.

Rooms can be arranged in different types to form clean room types. Something like Figure 9 is called a "ballroom" because we will have a large clean room (the whole workshop space is like a room in a ball). This type of room has a ceiling which is a high-performance air filter that provides airy to the whole workshop no matter where the machine is located. In fact, the best quality air is only really needed where the product turns in the direction where it can contaminate dust and in other areas it can accept a little less quality air. With this fact, one can create less expensive clean rooms and the other is the type into small rooms in a spindle - this type is called service chase. Each room will have a high standard of cleanliness, while the outer areas may have lower cleanliness. The children's rooms are located along a tunnel (this is the type of clean room I am working with). This clean room type has a much cheaper operating cost than ballroom style.

It is also possible to divide ballroom rooms into small functional rooms (Figure 10c) and, of course, in every small room there will be extremely high levels of cleanliness and service areas will have lower cleanliness. * Air filtration system for clean rooms [1.4] Clean room air must meet the requirements of dust particles level so dust filters are always required. Since 1980, a widely used filtration system called High Efficiency Particle Air (HEPA - High-performance particle filtration system). HEPA is a system capable of filtering dust particles in the air with an efficiency of 99.97% for dust up to 0.3m. Today, HEPA is also supplemented with features to filter bacteria and inert particles. (a) (b) A HEPA filter of deep folds (a) and small folds (b). The air is filtered through roll of filter paper into layers of filter media ranging in width from 15 to 30 cm and separated by thin aluminum foil. In order to prevent small dust particles, people use filter media as micro wires arranged in microscopic meshes and thus allow air to pass through, while blocking dust particles.

5. Equipment needed for clean room

People working in a clean room are a source of dirt for the room. When people move, it is possible to produce up to 100000 seeds (size greater than 0.5m) and thousands of micron-sized dust particles carry people every minute. Therefore, for every clean room, people have a limit on the number of people working in accordance with the size of the room. And to ensure the environment in the room, in addition to the machinery equipped for the essential work in the clean room, equipping people is essential to minimize the amount of dust produced. The necessary equipment for workers includes: - Protective clothing: Usually one-piece shirt and pants. - Protective helmet for the head beam (we remember human hair is also a source of dust) - Leg tight canvas shoes - Face mask, can have both air filter in mask, eye protection, Gloves shirts, hats, masks, shoes are usually made of fabric, with a smooth, non-dusty surface on the outside, while ensuring that people can easily move and operate.

In the field of physics, materials science, clean room is often used for the technology of manufacturing materials that require high purity such as optical etching, thin film technology (MBE, sputtering, CVD ...), component technology sold leads, electronic components, electronic microelectromechanical systems (MEMS, NEMS), delicate analysis, physicochemical processing ... Here, surely readers can answer the question "Why use Clean room? ”, if not answered, imagine, the technology for making components only micrometres to nanometers, just a small amount of dust can change the properties of the product completely. .

The first area when you enter the clean room is the dressing area. This is an intermediate chamber before coming to the function room, which is not clean. There, you will have to wear protective gear in accordance with the process and make sure not to contaminate the area before entering the work area. After finishing the work, before leaving the clean room, the employee must also remove the protective gear according to the process and leave the room.

6. Safe in clean rooms

In the clean room, in addition to the air cleanliness is controlled, the other factors are humidity must be controlled at a low level, pressure, temperature ... maintained at an appropriate level, ensuring sterility. Therefore, the first thing that every person working in a clean room must comply with is the labor safety rules to ensure safety. In developed countries, every person before working in a clean room has been very carefully learning the rules of working in a clean room, which were always at first the labor safety rules:

- How to get out of a clean room when there are unexpected accidents (fire, explosion, electric shock ...); The necessary handling for these accidents.

- How to minimize accidents and ensure occupational safety by using rules as well as working in the room scientifically and accurately.

- Rules to prevent contamination of rooms: remove items that can easily catch dust such as sweaters, beauties, warm gloves, jackets, etc. - Use, move, and remove chemicals and laboratory supplies Experiment properly.

- Use the equipment in the room properly.

Let us imagine making a mistake in the clean room rules, in addition to contaminating the room (which would be very harmful to the cleaning system), and at the same time it could be easy to cause accidents and damage and damage great about people and property. In England (I don't know how other countries are), before going to work independently in a clean room, workers must go through a course on occupational safety, signing a certificate of compliance with safety rules and pass the test of these rules to ensure clean room safety. Another annoying thing is that when working in a clean room, endure your own "sorrows", because clean rooms cannot allow you to create such dirt.

7. Conclusion

Clean rooms are an extremely sophisticated and modern working system, and it is no stranger to countries with advanced science and technology. In Vietnam, due to underdeveloped economic conditions and science, clean rooms are still very strange, and even though there are science-equipped units with clean rooms, I personally believe they are clean rooms. it cannot work because it requires running cost too high compared to the economic conditions of the units. Therefore, perhaps the clean room in Vietnam is still more "decorative" than bringing the research effect (hopefully my comment is wrong). As a researcher and also have to do many steps in the clean room, I personally hope that the clean room will soon become more popular in Vietnam so that the research people have the opportunity to develop and personally later return to the country have the opportunity to use the knowledge learned abroad.

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